The present invention relates to an electron beam lithography apparatus and more particularly to a correcting apparatus for correcting a lithographic distortion of the electron beam in high speed.
In the general electron beam lithography apparatus, the most popular one is an apparatus in which many marks is scanned by an electron beam so that positions of the marks are detected. At this time, the mark means a fiducial mark as a standard mark which is mounted on a stage mounting a wafer, and further the mark may be an alignment mark installed on the wafer. The detected positions of the marks are compared with previously measured positions corresponding to the detected positions which are previously measured by using a laser measurement system, and the deflecting current of the deflector is calculated so as to minimize the deflecting gain errors using a method of least squares.
That is to say, differences .DELTA.x and .DELTA.y between the detected positions of the marks and the previously measured positions (x,y) corresponding to the detected positions are calculated, optimum coefficients of the following equations (11), (12) are obtained using a method of least squares, and the deflecting current which corrects the positional errors .DELTA.x and .DELTA.y of the mark is calculated. EQU .DELTA.x=a.sub.00 +(a.sub.10 x+a.sub.01 y)+(a.sub.20 x.sup.2 +a.sub.11 xy+a.sub.02 y.sup.2)+(a.sub.30 x.sup.3 +a.sub.21 x.sup.2 y+a.sub.12 xy.sup.2 +a.sub.03 y.sup.3)+. . . (11) EQU .DELTA.y=b.sub.00 +(b.sub.10 x+b.sub.01 y)+(b.sub.20 x.sup.2 +b.sub.11 xy+b.sub.02 y.sup.2)+(b.sub.30 x.sup.3 +b.sub.21 x.sup.2 y+b.sub.12 xy.sup.2 +b.sub.03 y.sup.3)+. . . (12)
In the high order polynomial equations (11), (12), a.sub.00 and b.sub.00 are offset values, coefficients a.sub.10, a.sub.01, b.sub.10 and b.sub.01 of the first order variables correspond to deflective sensitivity error components as shown in FIG. 3(A) or rotational error components as shown in FIG. 3(B) which vary relatively in short time, coefficients a.sub.20, a.sup.11, a.sub.02, b.sub.20, b.sub.11 and b.sub.02 of the second order variables are an axial asymmetry components of the electron beam and coefficients a.sub.30, a.sub.21, a.sub.12, a.sub.03, b.sub.30, b.sub.21, b.sub.12 and b.sub.03 of the third order variables are pin/barrel distortion components.
Generally, setting many marks more than ten and detecting the positions of all of the marks, all of the coefficients in the equations (11), (12) are frequently calculated within a short cycle such as one hour or two hours in order to correct the deflecting gain errors of the electron beam lithography apparatus and it takes a pretty long time for every calculations performed frequently. Therefore, the working efficiency of the electron beam lithography apparatus became very low.
Furthermore, as marks on the specimen are scanned by electron beam in order to detect the positions of the marks, stains or blots are generated in the specimen chamber and contaminate the specimen so as to make the lithographic accuracy of the apparatus low. The Japanese Patent Laid-open No. 62-281246 is cited as an example of such apparatus.